JPS6340407A - Gain control circuit - Google Patents

Abstract

PURPOSE:To evade the danger that a gain is changed by a temperature, etc., by controlling the gain of a gain control means in accordance with the comparing result of the detecting output of a pilot signal component detecting circuit and a gain control signal. CONSTITUTION:A level V.X of a pilot signal component is detected by a pilot signal component detecting circuit 7 and it is inputted to the inverting input terminal of a differential amplifying circuit 8. Into the non-inverting input terminal of the differential amplifying circuit 8, a value V.A to multiply a gain control signal (the level is A) and a pilot signal is inputted. The difference between the V.A and the V.X is amplified by the differential amplifying circuit 8, and when the V.X is smaller than the V.A, the signal to increase the gain of a voltage variable resistance element 4 is sent from the differential amplifying circuit 8 to the voltage variable resistance element 4. Thus, a negative feedback loop is constituted of the voltage variable resistance element 4, a buffer 5, the pilot signal component detecting circuit 7 and the differential amplifying circuit 8. The gain of the voltage variable resistance element 4 is controlled so that the V.X can he always equal to the V.A.

Description

[Detailed description of the invention] The present invention will be described in the following order.

A. Field of industrial application B1 Overview of the invention C0 Prior art 1 Problem to be solved by the invention E0 Stage F to solve the problem F9 Effect G. Examples [Fig. 1, Fig. 2 1 H1 Effects of the Invention (A. Field of Industrial Application) The present invention relates to a gain control circuit, and particularly to a gain control circuit in which the gain is controlled as specified by a gain control signal, and there is no possibility that the gain will fluctuate due to temperature changes.

(B. Summary of the Invention) The present invention provides a synthesis circuit that adds a pilot signal outside the band to an input signal, and a synthesis circuit that adds a pilot signal outside the band to the input signal, in order to control the gain as specified by the gain control signal in the gain 1rl control circuit. A gain control circuit is constituted by a gain control means that passes through the output signal of the combining circuit, and a pilot signal component detection circuit that detects the level of the pilot I8 component of the output signal of the gain control means, and detects the pilot signal component. According to the gain control circuit of the present invention, the gain of the gain control means is controlled according to the comparison result of the detection result of the circuit and the gain control signal. This can be determined by the output of the pilot signal component detection circuit No. 8, and the gain of the gain control means is controlled based on the comparison result between the output of the pilot signal component detection circuit and the gain control signal. The gain r for the signal can be controlled, and the risk of the gain changing due to temperature or the like can be avoided.

(C, Prior Art) DAT (Digital Audio Data Recorder), Dv
There is a tendency for devices such as TRs (digital video tape recorders) to be required to perform various operations by remote control. Therefore, the audio level (sound!it) must also be controllable using a remote control. Conventionally, the audio level has been controlled by an electronic volume composed of an IC.

(D. Problem to be solved by the invention) By the way, with the current electric volume, when an audio signal is passed through it, a non-negligible distortion occurs when the volume is turned down.
+t There was a problem that it occurred at times.尤b? ff
When fif is not changed, the magnitude of distortion is not so large, and for example, when the volume gain 471 is about OdB, the distortion rate can be kept within the standard. However, when changing the 7T amount, the distortion became large, especially when turning down the volume.

Therefore, attempts have been made to control the volume using a voltage nJ variable low resistance element (CdS or the like) that does not cause distortion. A voltage variable resistance element using CdS or the like can not only reduce the distortion rate but also improve the frequency characteristics, so it can be said to be preferable in that respect. However, CdS
Voltage variable resistance elements using etc. have temperature drift,
There is a problem in that the volume changes little by little due to changes in temperature, and no effective solution to this problem has been taken in the past.

The present invention has been made to solve these problems, and provides a novel gain control circuit with low distortion, no temperature dependence, and capable of controlling gain as specified by a gain control signal. The purpose is to provide the following.

(E. Means for Solving the Problems) In order to solve the second problem, the gain control circuit of the present invention includes a synthesis circuit that adds a pilot signal outside the band to the input signal, and an output signal of the synthesis circuit. and a pilot signal component detection circuit for detecting the level of the pilot signal component of the output signal of the gain control means. The present invention is characterized in that the gain of the gain control means is controlled in accordance with the result of comparison with the Jlid control signal.

(F. Effect) According to the gain control circuit of the present invention, by adding a pilot signal to the input signal and passing it through one stage of gain control, the degree of amplification of the gain control means can be known from the output of the pilot signal component detection circuit. Then, based on the comparison result between the output of the pilot signal component detection circuit and the gain control signal, the gain of the gain control means is controlled, so the gain for the input signal can be controlled as per item a, It is possible to avoid the possibility that the gain changes due to temperature or the like.

(G, Embodiment) [FIGS. 1 and 2] Hereinafter, the gain control circuit of the present invention will be explained in detail according to the illustrated embodiment.

Figures 11-1 and 2 are for explaining embodiments of the gain control circuit of the present invention. Figure 1 is a circuit diagram, and Figure 2 shows the frequency relationship between the input signal and pilot signal. FIG.

In FIG. 1, 1 is a bypass filter that cuts the DC component of an input signal, which is an analog audio signal, and 2 is a pilot signal generation circuit that generates a pilot signal to be added to the input signal. Since the pilot signal must be separated after being added to the input signal, the frequency must be set to a frequency outside the frequency band of the input signal. Then, the sound t"' (the ri number is 2 as shown in Figure 2).
Since it has a dIF range of 0 to 20,000 Hz, the frequency of the pilot signal can be any value as long as it is outside that range, but in this embodiment, as shown in Fig. 2, a signal with a frequency of 0 is used as the pilot signal. , that is, direct current is selected. This is because the pilot signal is easy to generate and it is relatively easy to separate it from the input signals 1 and 3 after combining them into 11 input signals.

3 is a synthesis circuit that synthesizes Jinkai 1-1 and Pylon I/fli'J. In addition, V (lower case) in the figure indicates the level of the input signal at the stage when it is manually input to the synthesis circuit 3,
■ (Human character) reduces the level of the pilot signal at the stage when it is manually input to the synthesis circuit 3.

4 is a variable resistance element made of CdS or the like, and the gain can be controlled by the voltage.It has a very low distortion rate, and is better than 11. When the frequency is set, P1 is turned on. The signal output from the 71-variable 11°C resistor for the electric cable and the element r4 is sent to the buffer 5.
L, teba, rro-l- (manually powered by No. 73 removal circuit 6,
The pilot No. 411 (DC) component is completely removed from the signal by the signal removal circuit 6, and the gain-controlled input signal is used as the output signal of the gain control circuit.
The signal is sent out to the outside. In the figure, X indicates the gain of the voltage variable resistance element.

7 is the pylon [
- A pyro-soto signal component detection circuit that extracts only the signal (in this embodiment, only the DC component) and detects the level of the pilot signal component.

8 is a differential amplifier circuit, which sends the output of the multiplier circuit 9 that multiplies the gain control signal and the component detection circuit and an output signal indicating the pylon toy 1゛ζ to the voltage variable resistance element 4 as a signal for controlling the gain. do.

Next, the circuit operation of the 44I control circuit shown in FIG. 1 will be explained.

The input signal is inputted to a synthesis circuit 3 after its DC component is cut by a bypass filter 1 for DC cut. Further, the DC pilot signal generated from the pilot signal generation circuit 2 is also inputted to the combining circuit 3, the input signal and the pilot signal are combined in the combining circuit 3, and the input signal and the pilot signal are combined in the voltage variable resistance element 4. The signal obtained by combining the signals is gain controlled. If the amplification factor of the voltage variable resistance element 4 is set to The level of DC component) is V-X. .

Then, the level V- of the pylon l- (, - component
x is detected by the pilot component detection circuit and input to the inverting input terminal r of the differential amplifier circuit 8. Note: The gain control signal (its level The value V-A multiplied by A) and Pilot No. 45 is manually calculated.Then, the V-A and V-
X and y are amplified by the differential amplifier circuit 8, and
When it is smaller than lv-A, the voltage ■f becomes variable resistance I'
V-X or V-, like adding 11;1 to 4 points
When it is larger than A, the gain of the voltage variable resistor element 71 is lowered, and a strong signal is output from the differential amplifier circuit 8 to the voltage 11').
It is sent to variable resistance element r4.

However, L4, 7 "IF.I-1 just resistor element r4, buffer 5, pilot signal component detection circuit 7 and percussion amplifier circuit 8
A negative feedback loop is constructed, and always v−X or ■・A
The gain of the voltage variable resistance element r4 is controlled so that it is equal to Since the signal level is a constant known value, it can be said that the gain X of the voltage variable resistance element 4 is always controlled to be equal to the level A of the gain control signal.

Note that the gain control signal (a) does not necessarily have to be multiplied by the pilot signal by the multiplication circuit 9 before it can be compared with the output signal of the pilot signal removal circuit 7. For example, if the gain control signal itself is If the value of V-A is obtained without using the circuit 9, the multiplier circuit 9 is not necessary at all.What is shown in FIG. 1 is just one embodiment.

Then, the pilot signal component in the signal amplified by the voltage variable resistance element 4 is removed by the pilot signal removal circuit 6, and only the input signal component is multiplied by X, that is,
It is output to the outside as an audio signal at a level of v-x.

(H. Effects of the Invention) As described in Section 2 below, the gain control circuit of the present invention adds a pilot signal having a frequency outside the input signal frequency band and a predetermined level to the input signal. a synthesis circuit; a gain control means for passing the signal output from the synthesis circuit; and a pilot signal component for extracting a pilot signal component from the signal output from the gain control means and detecting the level of the component. Detection results and benefits of the par C lot signal component detection circuit, including at least a detection circuit. It is characterized in that the gain of the gain control means is controlled by a signal indicating the comparison result by comparing the I control signal with the I control signal.

Therefore, according to the gain control circuit of the present invention, by adding the pilot signal to the input signal and passing it through the gain control means, the amplification degree of the gain control means can be known from the output of the pilot signal component detection circuit, and the pilot signal The gain of the gain control means is controlled based on the comparison result of the output of the component detection circuit and the gain control signal, so the gain is 1F!
The gain relative to the input signal can be controlled in accordance with the control signal, and the risk of the gain changing due to temperature or the like can be avoided.

[Brief explanation of the drawing]

1 and 2 are for explaining one embodiment of the gain control circuit of the present invention. FIG. 1 is a circuit diagram, and FIG. 2 is a diagram showing the frequency relationship between the input signal and the pilot signal. be. Explanation of symbols 3...Composition circuit, 4...Gain control means, 7...Pilot signal component detection circuit. Mobu

Claims (1)

[Claims] (1) A synthesis circuit that adds a pilot signal having a frequency outside the input signal frequency band and a predetermined level to the input signal; a gain control means for passing the signal output from the synthesis circuit; and an output from the gain control means. gain control means, comprising at least a pilot signal component detection circuit for detecting the level of the pilot signal component from the signal detected by the pilot signal; A gain control circuit characterized by controlling the gain of